The invention relates to a method of processing, in particular manufacturing and/or repairing, a holding plate, which has a SiC-based surface and is provided for a clamping device (clamp, wafer chuck) for holding a component by electrostatic forces or low-pressure. In particular, the invention relates to a method of processing a holding plate, which is adapted for supporting a semiconductor component, e. g. a wafer, with electrostatic forces or by means of low-pressure, and which is provided with a structured surface with SiC-based surface elements (protrusions, e. g. protruding burls). The invention also relates to a method of manufacturing a clamping device being provided with the holding plate. The invention also relates to a holding plate with a structured, SiC-based surface with surface elements being arranged to hold a component, and to a clamping device with such a holding plate, in particular an electrostatic clamp or a vacuum clamp. Applications of the invention are e. g. in the manufacturing of tools, machines or wafers for the semiconductor industry.
It is generally known that integrated circuits (semiconductor chips) are produced by lithographic processing of semiconductor wafers which are held by a clamping device with electrostatic forces (electrostatic clamp) or by means of low-pressure (vacuum clamp). Further applications of clamping devices exist in inspection or measurement methods wherein, for example, the planarity of a wafer is determined. The clamping device comprises one or two holding plates with exposed surfaces for accommodating semiconductor wafers, as well as electrode devices, cooling devices and, if necessary, further electrical, mechanical or pneumatic components. With increasing integration density during chip production, extremely high demands are made on the planarity of the semiconductor wafers, for example in exposure steps, which must be ensured by the mechanical stability and the planarity of the surface(s) of the holding plate(s).
Since semiconductor wafers can be deformed in a disturbing manner even by dust particles on the surface of the holding plate, the holding plate is typically provided with a large number of protrusions, the free end sides (front faces) of which span a plane carrier surface. The projections comprise, for example, so-called burls. The burls have the advantage that the contact surface between the holding plate and the semiconductor wafer is minimized and eventually occurring dust particles can be collected in spaces between the burls. Furthermore, holding plates are typically made of a ceramic material, since ceramic materials are available with particularly high mechanical stability and strength.
In manufacturing a conventional clamping device, firstly the holding plate is made from the ceramic material with a free, flat surface. The burls are then formed by a material removal from the ceramic material. Various ablation methods are known for this purpose, such as cutting processes using a CNC milling machine, removal by means of die-sinking or removal by means of laser ablation (DE 10 2015 007 216 A1).
The conventional methods are characterized by the following disadvantages, especially in the production of burls with small diameters (e. g. 500 μm or smaller). Firstly, a relatively large amount of material has to be removed to provide the free-standing burls, which is time-consuming and energy-intensive. Undesired ceramic particles can occur in particular during machined processing and die-sinking and damage to the ceramic material can occur. Secondly, small processing errors, for example due to the omission of some burls during production, already can lead to the non-usability of the holding plate. In many practical applications of clamping devices in semiconductor processing, a vanishing error rate is required. Thirdly, processing errors or later damage to the holding plate cannot be corrected. With conventional techniques, it is not possible to restore an inadvertently damaged, e. g. broken off protrusion.
The above-mentioned problems of manufacturing holding plates occur not only with holding plates for wafer clamps with protruding burls, but also with holding plates for other tasks in which surface elements with more complicated shapes are formed.
Under the title “Silicone Carbide Growth using Laser Chemical Vapour Deposition”, Jian Mi, Josh Gillespie, Ryan W. Johnson, Scott N. Bondi, and W. Jack Lackey proposed the deposition of SiC by means of laser-based chemical vapor deposition at the “Solid Freeform Fabrication Symposium” in Austin, Tex., USA, 2003. Due to their small dimensions of only about 10 μm and highly irregular geometries, however, the resulting structures had no practical applications.